no trading with the enemy

The doctrine is not, at this day, to be questioned, that during a state of hostility, the citizens of the hostile states are incapable of contracting with each other. For near twenty years this has been acknowledged as the settled doctrine of this court, and in a case which proves it to be a rule of very general and rigid application... To say, that the rule is without exception, would be assuming too great a latitude... But at present, it may be safely affirmed that there is no recognised exception, but permission of a state to its own citizen, which is also implied in any treaty stipulation to that effect, entered into by the belligerents.